JPH0760739B2 - Modulated mixed dielectric film and electroluminescent device and optical disk - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a modulated mixed dielectric film, and more particularly to a film structure of a dielectric film suitable for use in a potential device such as an electroluminescence device and an optical disc. Is.

[Conventional technology]

It is important for application that the dielectric film has a high dielectric constant and a high breakdown electric field strength, but in general, these two are in a trade-off relationship. Therefore, as an improvement of the single film of SiO ₂ , Ta ₂ O _5, etc. in FIG. 1 (b), the laminated structure film of FIG. 1 (c) (Japanese Patent Laid-Open No. 52-129296) is used.
No.), and a further improvement thereof is the mixed structure film of FIG. 1 (d) (JP-A-59-224098).

[Problems to be Solved by the Invention]

However, even in the conventional mixed film structure, there is no consideration for utilizing the difference in the fracture characteristics of the single material used (which can be divided into self-repair type fracture and propagation type fracture if they are classified by force, but they are relative characteristics). Improvement of the breakdown electric field strength was insufficient.

It is an object of the present invention to provide a modulated mixed dielectric film in which the breakdown electric field strength and the thermal breakdown characteristics are improved by improving the mixed film structure, and an electroluminescence device and an optical disk to which this film is applied.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention is a dielectric film produced from at least two kinds of materials, wherein the mixing ratio of the film materials changes in the film thickness direction at a period of 5 to 300Å. A mixed dielectric film is proposed.

The film material is a combination of a material having a strong propagation type dielectric breakdown characteristic and a material having a self-repairing type dielectric breakdown characteristic.

Specifically, SiO ₂ , Y ₂ O ₃ , Si ₃ N ₄ , Sm ₂ O ₃ , Ta ₂ O ₅ , Ti
It is composed of at least two combinations of O ₂ , HfO ₂ , Al ₂ O ₃ , ZrO ₂ , X-TaO ₃ , X-NbO ₃ , and X-TiO ₃ (where X is a metal).

The present invention also proposes an electroluminescence device using the modulated mixed dielectric film having the above structure and components as at least a part of the insulating layer.

The present invention further proposes an optical disc using the modulated mixed dielectric film having the above structure and components as at least a part of the protective layer.

[Action]

In FIG. 1 (a) showing the concept of the structure of the modulation mixed dielectric film according to the present invention, the material A is a material having a high dielectric constant and a low breakdown voltage of propagation type breakdown, and the material B is a low dielectric constant and self-repairing type. Use a material with high breakdown voltage. Then, although the region (layer) containing a large amount of the material A has the characteristic of propagation type destruction, this region is set sufficiently thin and sandwiched by the region containing a large amount of the material B having the characteristic of self-repairing type destruction. As a result, the breakdown mode of the entire film can be made self-repairing. This is a result of improved stability to heat that causes the membrane to break.

Up to this point, the description has been divided into the extremes of propagation type breakdown and self-repair type breakdown, but in actual breakdown, many materials are self-repairing on the low voltage side and propagation type on the high voltage side. Since the breakdown electric field strength is determined by which voltage causes the propagation type breakdown, it is not always accurate to classify the materials into two types, and when comparing the two materials, one of the two materials with a more self-healing character is compared. It can be regarded as a strong material. When the method of modulation mixing is used for these two or more materials, the effect of the same concept as the case of modulating the materials of the propagation-type breakdown and the self-repair type destruction described above is obtained, and the thermal stability is obtained. Property and breakdown electric field strength are increased.

Now, in order to form the modulated mixed dielectric film, a film forming apparatus having two or more particle generation sources may be used, and a method such as sputtering, vapor deposition, MBE or CVD is used.

As a straightforward example, the steps of A material film formation → AB material film formation → B material film formation → AB material film formation → A material film formation ...

If the upper film material is implanted into the lower film material by ion plating or the like, a mixed film similar to the AB film simultaneous film formation in the above procedure can be formed.

These modulation structures can be confirmed by direct observation with a cross-sectional TEM (transmission electron microscope). Also, the thickness of each layer is 50Å
The above cases can be confirmed by SIMS (secondary ion mass spectrometry).

Further, the modulation period does not have to be constant in the film, and better properties can be realized by changing the film period depending on the application, the type of material, the film growth property, and the like.

〔Example〕

Next, an embodiment of the modulated mixed dielectric film according to the present invention will be described with reference to FIG.

FIG. 2 is a diagram showing the relative dielectric constant and the breakdown electric field strength of a film made of SiO ₂ having a strong self-repairing destructive character and TiO ₂ having a strong propagating type destructive character. This film is composed of SiO ₂ tarts and TiO ₂
The target and the target were alternately sputtered. SiO ₂ and Ti
The calculated film thickness with O ₂ is 9Å for each calculation.
And 3Å, 30Å and 10Å, 60Å and 20Å, 150Å and 50Å, 300Å and 10
Layers were repeatedly laminated until the total film thickness reached 5000Å, with 0Å, 1800Å and 600Å each. In this case, due to the effect of implanting sputtered particles into the film, a mixed layer of SiO ₂ -TiO ₂ is formed at the boundary between SiO ₂ and TiO ₂ , and that layer is used for measuring the light absorption edge. Therefore, it is estimated to be about 10 to 20Å.
As shown in FIG. 2, the dielectric constant is almost constant, but the breakdown electric field strength is improved in the region where the calculated thickness of the TiO ₂ layer is 100 Å or less. This value is the breakdown electric field strength of the homogeneous mixed film prepared by using the TiO ₂ -75% SiO ₂ mixed target (second
It is larger than the arrow position on the left side of the vertical axis in the figure). That is, 300Å
In the films having the following periods, the characteristic improvement due to the modulation mixing effect is recognized. If the modulation period thickness is made too thin, the thickness becomes close to that of the conventional mixed film, so the lower limit is set to 5Å here.

FIG. 3 shows a cross-sectional structure of an embodiment of a thin film EL (electroluminescence) element to which this modulated mixed dielectric film is applied.
1 is a glass substrate, 2 is a transparent conductive film (200 nm thick), 3 is a first insulating layer (500 nm thick), 4 is a light emitting layer (ZnS: 0.5 wt% Mn, 500)
nm thickness), 5 is the second insulating layer (500 nm thickness), 6 is the back electrode (2
(00 nm thickness). The emission start voltage and the element breakdown voltage by the 1 kHz sine wave of the EL element in which the TiO ₂ / SiO ₂ modulation mixed film whose characteristics are shown in FIG. ₂ are applied to the first and second insulating films of this thin film EL element are Shown in the figure. The white circles are the light emission start voltage, the black circles are the element breakdown voltage, and the difference between the two is the drive voltage margin. For stable driving, it is necessary to increase the driving voltage margin, but as shown in FIG. 4, the driving voltage margin increases in the region of 300 Å cycle or less.

FIG. 5 shows an embodiment in which the modulation mixed film of the present invention is used as the protective layer of the magneto-optical disk.

The protective layer sandwiching the recording layer of the magneto-optical disk from one side or both sides is required to have a high refractive index, mechanical strength, thermal stability, low thermal conductivity and the like. The mixed insulating film is effective as this protective layer in the sense that the advantages of the single film are combined, but the thermal stability can be further improved by using the modulated mixed dielectric film of the present invention. FIG. 5 shows the cross-sectional structure of a rewritable optical disc. Reference numeral 10 is a polycarbonate substrate, 12 is a GdTbFe recording layer (50 nm thick), and 11 is a protective layer (10 nm thick) to which the modulation mixed film according to the present invention is applied. TiO ₂ 10 by sputtering
Å (calculation) and SiO ₂ 10 Å (calculation) are laminated alternately,
A modulated mixed film is created by the effect of implanting sputtered particles into the film. As a result, in addition to the high refractive index of TiO ₂ and the excellent mechanical strength of SiO ₂ , the thermal stability was further improved.

〔The invention's effect〕

According to the present invention, the breakdown electric field strength of the mixed dielectric film can be improved. Therefore, it is possible to use a new material in which a material having a high dielectric constant, which is difficult to use because the breakdown electric field strength is too low, is mixed with a material having a high breakdown electric field strength. In particular, it is effective for devices such as EL display devices that require an insulating film having both a dielectric constant and a high breakdown electric field strength.

In order to show a concrete effect, the modulation mixed film prepared by sputtering (calculated, the relation between the breakdown electric field strength of TiO ₂ 10Å−SiO ₂ 30Å and the total film thickness 7 and the mixed film (TiO ₂ : SiO ₂ =
Figure 8 shows the relationship 8 between the breakdown electric field strength and the film thickness in 3). The effect of the present invention is remarkable for two or more cycles.

[Brief description of drawings]

FIG. 1 (a) is a conceptual diagram of the structure of a modulated mixed dielectric film according to the present invention, (b) is a conventional single film, (c) is a conventional laminated film,
(D) shows a conventional mixed film, and Fig. 2 shows Ti.
FIG. 4 is a diagram showing the relative permittivity and the breakdown electric field intensity with respect to the modulation mixing period of a film in which multiple layers are mixed by sputtering O ₂ : SiO ₂ = 1: 3. FIG.
The figure shows the emission start voltage and the element breakdown voltage when the modulation mixed dielectric film of FIG. 2 is adopted as the insulating layer of the EL element of FIG. 3, and FIG. 5 adopts the modulation mixed dielectric film as the protective layer. FIG. 6 is a diagram showing the prepared optical disc, and FIG. 6 is a diagram showing the breakdown electric field strengths of the modulated mixed dielectric film and the conventional mixed film in comparison. 1 ... Glass substrate, 2 ... Transparent conductive film, 3 ... First insulating layer, 4 ... Light emitting layer, 5 ... Second insulating layer, 6 ... Back electrode, 7 ... Modulation mixed dielectric film destruction Electric field strength, 8 ... Breakdown electric field strength of conventional mixed film, 10 ... Polycarbonate substrate, 11 ... Protective layer, 12 ... GdTbFe recording layer.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Kazuo Taguchi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Works, Ltd., Hitachi Research Institute (72) Akira Sato 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Works Co., Ltd. Within Hitachi Research Laboratory (72) Kenichi Hashimoto 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Inventor Yoshio Abe 4026 Kuji Town, Hitachi City, Ibaraki Hitachi Research Institute, Ltd. ( 72) Inventor Masanobu Hanazono 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Co., Ltd. (56) References JP-A-52-129296 (JP, A) JP-A-59-224098 (JP, A) Special Kai 53-43700 (JP, A) JP 58-194206 (JP, A) JP 60-121605 (JP, A) JP 62-133605 (JP, A) Kai 62-188038 (JP, A) JP 63-26995 (JP, A) JP 63-289793 (JP, A) JP 58-212119 (JP, A) JP 49-33756 ( JP, B1)

Claims (5)

[Claims] 1. A modulated mixed dielectric film, comprising: a dielectric film made of at least two kinds of materials, wherein a mixing ratio of the film materials changes in a film thickness direction at a period of 5 to 300Å. 2. The modulated mixed dielectric film according to claim 1, wherein the film material is a combination of a material having a strong propagation type dielectric breakdown characteristic and a material having a self-repairing type dielectric breakdown characteristic. Modulated mixed dielectric film. 3. The modulated mixed dielectric film according to claim 1, wherein the film material is SiO ₂ , Y ₂ O ₃ , Si ₃ N ₄ , Sm ₂ O ₃ , Ta ₂ O ₅ , TiO _{2.
2, HfO 2, Al 2 O} 3, ZrO 2, X-TaO 3, X-NbO 3, modulating mixed dielectric film X-TiO ₃ (where X is a metal), characterized in that it consists of at least two combinations of . 4. An electroluminescent device, wherein the modulated mixed dielectric film according to claim 1, 2 or 3 is used as at least a part of an insulating layer. 5. An optical disc comprising the modulated mixed dielectric film according to claim 1, 2 or 3 as at least a part of a protective layer.